The present invention relates to transmission control systems for automobiles.
A prior-art transmission control system for an automobile is so constructed that a vehicle speed and a throttle valve opening are sensed as electric signals, and that a predetermined shift gear corresponding to the current values of the vehicle speed and the throttle valve opening is selected on the basis of a shift pattern which is preset, with the vehicle speed and the throttle valve opening as variables. Herein, a plurality of such shift patterns are set beforehand, and one of them is selected by the manipulation of the driver of the automobile.
In another transmission control system, the shift patterns are automatically selected and changed-over in accordance with the driving operation of the driver.
The control of a transmission in the prior art is such that a predetermined gear position corresponding to the current values of a vehicle speed and a throttle valve opening is selected on the basis of a shift pattern which is preset, with the vehicle speed and the throttle valve opening as variables.
In addition, the official gazette of Japanese Patent Application Publication No. 45976/1988 discloses a technique wherein a torque is evaluated from the pressure of an intake pipe, and a transmission gear ratio [(r.p.m. of an internal combustion engine)/(vehicle speed)] is determined from the torque.
These methods have made performing an exact shift operation for the fluctuations of drive conditions difficult, especially for the change of a running load. For example, it is considered that the fuel consumption of the automobile will be enhanced without spoiling the drivability thereof, by upshifting earlier on a flat road or a gentle downward slope rather than on an upward slope. Such a shift operation, however, has heretofore been impossible because of the gear shift based on only the throttle valve opening and the vehicle speed.
Besides, as the vehicle is lightened, it becomes important to perform the shift control so as to correspond to the change of acceleration characteristics dependent upon the weight of the vehicle in the case of a starting acceleration. It is therefore considered possible to enhance the fuel consumption and to perform the exact shift operation corresponding to the drive conditions, in such a way that the running load and the vehicle weight are estimated, and that the shift pattern is changed in accordance with the vehicle weight and the running load in an accelerating mode, while it also is changed in accordance with the running load in a decelerating mode.
Since the shift pattern is determined on the basis of the several typical drive conditions as stated above, the prior-art techniques have been sometimes incapable of the shift operation which reflects the drive conditions exactly. As a result, they have often worsened the fuel consumption.